Field of the Invention
The present invention relates to an intake system of an internal combustion engine and, in particular, to an intake system of an internal combustion engine including a plasma actuator provided in an intake passage.
Description of the Related Art
For example, in an internal combustion engine for a vehicle, there is known an intake system including a fuel injection valve that injects fuel to an intake passage. In this case, fuel injected from the fuel injection valve adheres to an inner wall surface of the intake passage.
Japanese Patent Laid-Open No. 2014-001691 discloses that in order to suppress adhesion of injected fuel to an inner wall surface of an intake passage and to promote vaporization of the fuel, gas (an air) is supplied from a gas supply mechanism toward a portion to which the injected fuel adheres in the inner wall surface of the intake passage.
By the way, usually, fuel injection from the fuel injection valve is started before valve opening of the intake valve, i.e., during valve closing. In that case, the fuel injected from the fuel injection valve to adhere to the inner wall surface of the intake passage tends to flow down along the inner wall surface of the intake passage, and to be accumulated in a concave portion sandwiched between the inner wall surface of the intake passage and the intake valve. The accumulated fuel flows into a combustion chamber in a cylinder at once at the time of valve opening of the intake valve. Accordingly, there is a problem that the fuel having become comparatively large droplets vaporizes in the combustion chamber, and thus vaporization of the fuel is delayed, and as a result, much HC as unburned fuel is discharged.
This is particularly remarkable at the time of cold operation of the internal combustion engine. It is because at the time of cold operation, a temperature of the inner wall surface of the intake passage is low, and thus vaporization of adhesion fuel by receiving heat from the inner wall surface of the intake passage is apt to be insufficient.
Note that since the gas supply mechanism described in Japanese Patent Laid-Open No. 2014-001691 supplies high-pressure gas to a portion to which injected fuel adheres from an upstream side of the portion, the supplied high-pressure gas may wash away the adhesion fuel to a downstream side to thereby promote the above-described problem.
Consequently, the present invention has been devised in view of the above-described circumstances, and an object thereof is to provide an intake system of an internal combustion engine that can prevent fuel injected from a fuel injection valve to adhere to an inner wall surface of an intake passage from going to a downstream side of the intake passage.